float sdBox(in vec2 p, in vec2 b){
    vec2 d = abs(p) - b;
    return length(max(d, 0.)) + min(max(d.x, d.y), 0.);
}

void mainImage(out vec4 fragColor, in vec2 fragCoord){
    vec2 uv = fragCoord / iResolution.xy;
    uv = (uv - .5) * 2.;
    uv.x *= iResolution.x / iResolution.y;

    uv *= vec2(2., 2.);
    float d = sdBox(uv, vec2(.6, .3));
    float c = smoothstep(0., .02, d);
    fragColor = vec4(vec3(c), 1.);
}